compile base_screen.cpp separately for {pcbnew,cvpcb} and eeschema, so we can diverge internal units at compile time, not runtime

Pcbnew: fix a serious bug: crashes when attempt to modify a zone that had lost its net (after eeschema changes for instance)

keep all the labelling tools together in the eeschema toolbar.

portrait setting was being overwritten in dialog_page_settings.cpp, add updatePortrait(), improve comments

    sizes.  Tested with postscript output only.  Required minor file format changes
    to reflect the "portrait" setting.  common/dialogs/dialog_page_settings.cpp
    uses a checkbox but its name is "Landscape", which is inverted from portrait,
    but since it is the more common choice, I used that rather than portrait.
    The tooltip for that checkbox makes it clear.  No portrait mode is supported
    for "User" paper size.

* Remove unnecessary copy constructors from board and module library
  objects.
* Add doClone() method to board and library objects.
* Add comment to class definitions where the default copy constructor
  generated by the compiler was adequate.
* Replace copy method with clone method where applicable.
* Remove DuplicateStruct() function.
* Remove track object copy function.

Eeschema: Fix erroneous message [Read Only] after creating a new project, and obviously the corresponding schematic file does not yet exist (replaced by [no file])

Gebview: fix issue in export to pcbnew (Track arc shapes are now exported, approximated by segments)

Pcbnew: fix issue when KICAD_NANOMETER is defined: when zones use htcth to show zones areas, hatch lines were incorrectly calculated (hunded of thousand lines created)
Eeschema: fix issue in search: search not made in reference strings.
Minor fixes, code cleaning and comment enhancements.

* Remove unnecessary copy constructors from schematic and component
  library objects.
* Add comment to class definitions where the default copy constructor
  generated by the compiler was adequate.
* Add assignment operator to EDA_ITEM, SCH_ITEM, and all schematic
  objects where the default assignment operator generated by the
  compiler would not be adequate.

  * Carve out TITLE_BLOCK from BASE_SCREEN
  * Add include/hashtables.h and put class PROPERTIES in there.
    Change PROPERTIES to use "const char*" as the key instead of wxString.
++eeschema
  * Add shim class SCH_BASE_FRAME which introduces the data model SCH_SCREEN
    to the frame EESCHEMA frame class hierarchy and allows sharing of:
    SCH_SCREEN* GetScreen() const;                              // overload EDA_DRAW_FRAME
    void SetPageSettings( const PAGE_INFO& aPageSettings );     // overload EDA_DRAW_FRAME
    const PAGE_INFO& GetPageSettings () const;                  // overload EDA_DRAW_FRAME
    const wxSize GetPageSizeIU() const;                         // overload EDA_DRAW_FRAME
    const wxPoint& GetOriginAxisPosition() const;               // overload EDA_DRAW_FRAME
    void SetOriginAxisPosition( const wxPoint& aPosition );     // overload EDA_DRAW_FRAME
    const TITLE_BLOCK& GetTitleBlock() const;                   // overload EDA_DRAW_FRAME
    void SetTitleBlock( const TITLE_BLOCK& aTitleBlock );       // overload EDA_DRAW_FRAME

    Add shim class SCH_BASE_FRAME which introduces the data model SCH_SCREEN
    to the frame class hierarchy.

rather than being rejected.

This feature is very useful for electronics hobbyists who use DIY PCB technology 
(both toner transfer and photoresist methods).
Also width correction may be useful for PCB designers who take care of track width etching.
This patch also fixes some minor PS plotting issues.